Effect of Ti4+ on the structure of nepheline (NaAlSiO4) glass

Abstract

In this study, the effect of Ti 4+ on the structure of nepheline glass (NaAlSiO 4) is investigated as SiO 2 is systematically replaced with TiO 2. Traditionally, TiO 2 is considered to be a nucleating agent for silicate crystallization but can also be incorporated into the glass network in relatively large amounts as either a glass former or modifier depending on its coordination with oxygen. To determine the effect of Ti 4+ on the structure of nepheline glass, X-ray and neutron pair distribution function (PDF) analysis paired with Empirical Potential Structure Refinement (EPSR) were conducted and are supplemented with Raman spectroscopy and Ti Kedge X-ray absorption spectroscopy (including Extended X-ray Absorption Fine Structure, EXAFS). Through these methods, it has been found that up to 15 mol% (16 wt%) TiO 2 can incorporate into the glass network as a primarily four-fold coordinated species, with a minor contribution of five-fold coordinated Ti as the TiO 2 content is increased. Between NaAlTi 0.1 Si 0.9 O 4 and NaAlTi 0.2 Si 0.8 O 4 , EXAFS suggests a local structure change in the second nearest neighbor, from a Ti atom to an Al atom. Raman spectroscopy also suggests that as Ti content increases, the Na environment becomes more ordered.

Redox-induced crystallisation in Ti-bearing glass-forming melts: A Ti K-edge XANES study

“…The LO, CT50.05 and NAT50.25.18 glasses were prepared following [7]. The ULE® glass was made by Corning Inc. (Corning Code 7972).…”

“…Nominal glass compositions are reported in Table 1. Unpolarized Raman spectra were recorded using a T64000 Jobin-Yvon ® Raman spectrometer and a Coherent ® Innova 70-C5 Ar + laser operating at 514.532 nm [7,10]. In-situ Ti K-edge XANES data were collected on the DiffAbs beamline at SOLEIL synchrotron, France.…”

“…The samples were oriented at 45° from the incident beam, in the microfurnace [ 7 ]. T emperature can be varied up to 2000 K with a precision of ± 10 K [ 7 ] . values are estimated from the nominal oxygen concentration in each gas .…”

“…TiO 2 -bearing glasses and glass-ceramics have applications in several fields including biomaterials, laser materials and optical fibres [2][3][4]. In glasses, Ti is usually tetravalent (e.g., [5][6][7]). Ti 3+ may appear under very reduced conditions, potentially relevant for the young Earth [8] or for material properties [9].…”

“…In the present study, Ti K-edge XANES experiments are conducted on melts equilibrated at high temperature in a micro-furnace [7,10] with a controlled atmosphere. Four compositions were studied: one synthetic analogue of the Lunar Orange glass collected during the Apollo missions (LO glass), a wollastonite composition containing 5 mol% TiO 2 (CT50.05), a Ti-bearing nepheline composition (NAT50.25.18), and the SiO 2 -TiO 2 ULE glass from Corning Inc. Those compositions were selected because (i) the LO and ULE glasses represent natural and industrial Ti-rich compositions, respectively, and (ii) the CT50.05 and NAT50.25.18 are glasses with well-known structure containing different Al concentrations and also different network-modifying cations (Ca and Na).…”